With the advent of “smart home” systems, household lighting can be remotely controlled from within or outside the home through available wi-fi connections. Z-wave controllers are a particularly advantageous component of such systems, for several reasons. Due to their “mesh network” capabilities, each Z-wave device can act as a repeater and can directly communicate with other associated devices without going through a central hub. A Z-wave hub can interface with wi-fi and Bluetooth devices to enable remote control, including voice control, of lighting. Moreover, since available Z-wave modules incorporate both RF transceivers and microcontrollers, they provide in one unit both the communications link to other devices and the lighting control functions for connected multi-way switches.
In order to perform these functions, however, the Z-wave module must be constantly connected to an active low voltage DC power supply drawing from an AC line. This requirement is problematic in a conventional multi-way lighting circuit, in which no power is provided to any of the switches when power to the lighting load is turned off. Some prior art smart switches address this problem by pairing the smart switch with a specially designed remote switch, which increases the expense and difficulty of the installation. Other multi-way smart switch designs do not require replacement of the remote switches, but instead require rewiring so that the power to the smart switch can by-pass the remote switches when the load is powered off.
Another approach to this problem is disclosed in U.S. Pat. No. 8,212,425 of Mosebrook, et al., which is incorporated herein by reference. FIG. 5A of that patent depicts a smart dimmer (502) in which the power supply (520) is connected in series with the mechanical three-way remote switch (504) and lighting load (508) alternately through one of two diodes (522, 524), so that the power supply (520) alternately draws current through one of the two dimmed hot terminals (DH1 or DH2), depending on the A or B position of the remote switch (504) (column 12, lines 5-15). But this arrangement has the distinct disadvantage of interrupting current flow to the power supply when the remote switch (504) is transitioning between positions A and B or gets stuck in a “dead travel” position where the movable contact is not engaging either of the fixed contacts. The Mosebrook disclosure acknowledges that, because of space limitations, it's not feasible to incorporate into the power supply a sufficiently large storage capacitor to bridge these switch transitioning power interruptions (column 13, lines 14-44).
Therefore, there is a need, as yet not fully addressed by the prior art, for a smart multi-way switch that is reliably always powered on while the AC line is active. The present invention addresses this need, while also improving the efficiency of the smart switch by using a Z-wave module to integrate the switch's load control and communications functions.